Just like our original thoughts on which catamaran to go with, our current choice for a dinghy has evolved over time. Let's use the way back machine and go back about ten years to when we were thinking about which type of cat we wanted to buy (someday).
Initially, we were looking at a custom-built, Kurt Hughes designed, catamaran (see right). We even had this half-finished one picked out. (Note, someone else bought and finished her and is now out sailing the world.) She was 58' long.
At that time, we thought that a light, narrow hulled, faster cat was just what we wanted! Then, over time, we slowly came to realize that comfort trumps speed. With all the people and sports toys we want to have with us, we would over loaded a fast cat, turning it into a slow cat. Instead, by starting with a cat with wider hulls that is designed for load carrying capacity, we could get almost the same speed out of it as the overloaded (previously) fast cat. We figure, if we are only going to go at 8 knots anyway, why not have all the space and comforts?
The more we looked at this, the more our choices changed to the two boats we are currently interested in buying. (For more on cats, see 'Best Cat for Us' on our www.svlynx.com website). However, here is a picture of one of the cat models we are currently interested in buying (see below, left).
Now, our choice in a dingy is going through a similar evolution. Initially, we were interested in a big tender with seats, a steering console, and a big-assed powerful gas outboard. Now reality has started to set in. If we buy such a tender, with the motor, she will weigh in at over 600 lbs, possibly over 700. There are three major issues with that.
1) That adds a lot of weight to our catamaran, and though our comfy style 'fat cat' can handle a lot of weight, there are still limits, and the lighter she is, the faster she will go (up to a point).
2) It puts an extreme amount of weight on the stern. That isn't good. The stern is designed to handle a certain amount of load. Too much will shove the sugar scoops down and cause hobby horsing as we sail.
So, that means we have to put our future tender on a diet and lose some significant amount of weight.
Here is the conundrum. A small dinghy, with a tiny outboard, is nice and light for the catamaran and can be beached easily (see pic right). It is also frugal on the use of gasoline, which means we don't have to store a lot of flammable and (sometimes) hard to get fuel onboard the mothership. But, that small light dingy with its tiny outboard can't go great distances at a decent speed. What happens when we want to load up some dive gear and divers, and then motor to a distant dive site, far from where our main catamaran is anchored?
We have found a compromise we can live with. First off, we are going to go with an electric propulsion system. At first glance, this might seem foolhardy, since gas packs a whole lot more energy by weight than batteries. This is true. However, I will get to more about this in a moment.
If we go with a large yet light dingy, we have figured out a way to have our cake and eat it too! The boat can even have a few comforts, like a twin floor to keep stuff (and your feet) from sitting in water. If the dinghy is around 12' long, it fits between the sugar scoops. If the weight is kept down to under 200 lbs, we can drag it up onto a beach (adding dinghy wheels to the transom to help us). That's the boat only weight, so what about the motor and fuel source?
In exchange, we have to accept a smaller motor and our fuel source will not take us as far at high speed. Battery power will take you a long distance, but at the cost of speed. If you want to go fast, then you sacrifice range. Most of the time that's fine. We won't often be taking the dinghy for extremely long distances. With a 48volt battery pack, with 300 amps, Our a 25 hp equivalent electric motor, we should go for about one hour at full speed traveling about 18 miles.
Just to note, if we cut the speed in half, we can go about six to eight hours instead of one. If you figure we are going from 18 mph, full out, to about 9 mph, at half speed, you can see how you extend your range. Full out, you go 18 miles. At half throttle, you go more like 100 miles. Now, we don't think that will hold completely true, those kinds of simple power calculations don't account for ocean conditions, etc., but if we figure we go even half that, 50 miles, that is still a decent range which is sufficient for our needs.
Best yet, we don't have to buy or store gas anywhere.
Let's get back to talking about how we can have a boat that goes far with a decent amount of people and gear, yet can also be easily beached. Generally, most of the boats we have seen out there do one of three things. They have a small dinghy with a tiny motor and give up the gear and people going long distances. Or, they have a bit dinghy with a powerful gas motor, yet give up beaching the boat. Finally, there are compromise boats, where they are just light enough to beach and just powerful enough to go plain. The problem with these boats is that as soon as you put much weight in them they no longer plain.